This invention relates to an improved process for reacting allyl chloride, water and chlorine to produce dichlorohydrin. "Dichlorohydrin" is a term employed herein to designate the isomers 1,2-dichloro-3-hydroxypropane and 1,3-dichloro-2-hydroxypropane.
It is known to prepare an aqueous solution of dichlorohydrin by reacting in a reaction zone allyl chloride, water and chlorine in dilute aqueous phase.
U.S. Pat. No. 2,714,121, incorporated herein by reference, discloses producing halohydrins by using high dilution of e.g., 250 to 400 volume of water per volume of e.g., a halosubstituted hydrocarbon in aqueous medium with subsequent addition of the halogen, and keeping the organic by-product phase dispersed as fine particles.
U.S. Pat. No. 2,714,123, incorporated herein by reference, discloses producing an aqueous solution of dichlorohydrin in a series of reaction stages wherein substantially all of the water is fed to the first of the reaction stage and the other reactants added in substantially equimolar proportions into each of the reaction stages.
U.S. Pat. No. 3,909,382 discloses recovering acid values, such as hydrochloric acid formed during olefin chlorohydrination, by series flow through a plurality of electrodialysis stages to upgrade the acid to higher concentration.
From Japanese Patent No. 74,00369 it is known that the product mixture from the reaction of a lower olefin, chlorine and water can be electrodialyzed to remove the by-product ions of hydrogen and chlorine, and the ion-depleted chlorohydrin solution circulated to the single reaction zone, enabling the production of a concentrated aqueous chlorohydrin solution.
As disclosed in copending Application Ser. No. 814,331, filed Dec. 27, 1985, in a multistage reaction system increased selectivity to the desired dichlorohydrin may be obtained by electrodialyzing the reaction effluent of one stage prior to being fed to a subsequent stage. Such electrodialyzing is advantageously carried out by neutralizing the removed acid in the concentrate stream of the electrodialysis zone as disclosed in copending Application Ser. No. 814,333, filed Dec. 27, 1985. A disadvantage of such procedures is that the electrodialysis membranes are somewhat permeable to the desired dichlorohydrin product and other haloorganics resulting not only in yield loss to the concentrate stream or streams, but also that the presence of such haloorganics in the aqueous concentrate stream requires energy intensive treatment to reduce the amount of organics to levels acceptable in receiving bodies of water such as rivers, lakes and the like. A further problem is that in the electrodialysis of hydrochloric acid, current efficiency becomes lower with increasing differences in hydrochloric acid concentration between the concentrate, i.e., ion receiving stream and the diluate i.e., ion depleting stream. The present invention provides a solution to these difficulties.